public class Mirror {
    // 二叉树的镜像
    // https://www.nowcoder.com/practice/a9d0ecbacef9410ca97463e4a5c83be7?tpId=295&tags=&title=&difficulty=0&judgeStatus=0&rp=0&sourceUrl=%2Fexam%2Foj%3Fpage%3D1%26tab%3DSQL%25E7%25AF%2587%26topicId%3D295
    public TreeNode Mirror (TreeNode pRoot) {
        // write code here
        if (pRoot == null) {
            return  null;
        }
        TreeNode leftResult = Mirror(pRoot.left);
        TreeNode rightResult = Mirror(pRoot.right);
        TreeNode tmp = pRoot.left;
        pRoot.left = rightResult;
        pRoot.right = tmp;
        return pRoot;
    }
}
